1. Field of the Invention
This invention relates to a thermally developable photosensitive material, in particular, which is stabilized to light and heat.
2. Description of the Prior Art
Photographic processes using silver halides have superior photographic properties such as photosensitivity and gradation as compared with electrophotographic processes and diazotype photocopying processes. However, the silver halide light-sensitive materials used in the photographic processes are developed with developing solutions and then subjected to several processings such as stopping, fixing, washing with water and stabilizing in order to prevent the developed images from discoloring or fading under normal light and to prevent the nondeveloped areas (which will hereinafter be referred to as "background") from blackening. Therefore, these processings are time consuming and laborious and, in addition, create a problem in that the handling of chemicals is hazardous to the human body and the chemicals contaminate the processing rooms and the hands and clothes of the workers. In the photographic process using a silver halide, it is very desirable to carry out the processings in a dry condition without using solutions and to stabilize the processed image.
To this end, various approaches have hitherto been made. For example, the first approach is the so-called one bath developing and fixing method wherein the development and fixing in the silver halide photographic process of the prior art are carried out in one operation, as described in U.S. Pat. No. 2,875,048, British Pat. No. 954,453 and German Pat. No. 1,163,142. The second approach is an effort to carry out in a dry condition the processings of the silver halide photographic process which have hitherto been carried out using a wet process, as described in German Pat. No. 1,174,159 and British Pat. Nos. 943,476 and 951,644. The third approach is an effort to use a light-sensitive element consisting mainly of a silver salt of an aliphatic carboxylic acid such as, for example, behenic acid, silver saccharin or silver benzotriazole with a catalytic amount of a silver halide, as described in Japanese patent publications Nos. 4921/1968, 4924/1968, 26582/1969, 18416/1970, 12700/1970 and 22185/1970 and British Pat. No. 1,205,500.
The present invention relates to the third approach of the above described three approaches.
It is known that when a thermally developable photosensitive material obtained by coating onto a support in a monolayer or as multilayers (a) a non-photosensitive and reducible organic silver salt such as silver behenate or silver benzotriazole, (b) a very small amount of a photosensitive material, that is, silver halide or an inorganic halide which forms a light-sensitive silver halide by reaction with the non-photosensitive silver salt (a) and (c) a reducing agent with (d) a suitable binder is used, a stable image can be obtained by exposing and then developing in a dry process without fixing and other processings. The so thermally developed image can be maintained stable for a sufficiently long time at room temperature even under exposure to white light without subjecting the material to a subsequent fixing or stabilization, but, when the material is stored at a high temperature and high humidity, in particular, under exposure to white light, a slight development proceeds gradually and the background gradually turns brown. Therefore, the nonexposed area must be stabilized, in particular, where a copy which is to be stored permanently is desired.
In order to solve this problem, a proposal has been made to improve the photosensitive material imagewise exposed and thermally developed by treating the material with a solution containing a stabilizer as disclosed in Japanese patent publication No. 5393/1971. That is to say, this method for the stabilization of a developed image of a thermally developable photosensitive material, which comprises a dispersion in a binder (d) of the four components of (a) silver benzotriazole, (b) at least one of a silver halide and an inorganic halide capable of forming a silver halide by reaction with (a), (c) a reducing agent and (e) an organic carboxylic acid or a salt thereof, in which the resulting dispersion of these components has been coated onto a support in a monolayer or as multilayers, comprises treating the resulting thermally developable photosensitive material, after exposure and thermal development, with a stabilizing solution containing an organic compound represented by the following general formula, EQU X C --0 SH or X C = S
however, this method destroys a feature of the thermally developable photosensitive material in that when such a treating solution is used, the method is no longer a dry process.
On the contrary, this invention does not need any treating solution and thus the dry processing aspects of the thermally developable sensitive material are retained.